ovens may be either electric
infrared or gas infrared. We have the unique
ability to discuss both: Because we use both. We have
a wealth of infrared experience to assist you.
infrared ovens use gas burners, or sources. Gas infrared
sources typically burn a fuel/air mixture to heat
a metal or ceramic to an incandescent temperature.
The following descriptions highlight the most common
sources for gas infrared ovens.
intensity impingement burners. Impingement burners,
available in a variety of shapes and sizes, radiate
flame energy from refractory ceramics of various shapes.
Typically, the sources offer a source temperature
of 1,200 to 1,900°F and a heat intensity of 10,000
to 50,000 BTUs per hour per square foot. They typically
appear red to orange during operation, heat up in
15 to 90 seconds, are resistant to thermal and physical
shock, and have a typical radiant efficiency of 30
burners are generally not susceptible to preignition,
or flashback, and resist physical damage but have
relatively low radiant efficiencies. They effectively
resist damage from falling parts and are also effective
in multipass ovens where cooling air cannot be provided
at the rear of the burner. Life expectancies are measured
in years, unless the burner is subjected to overfiring.
intensity porous matrix burners. Porous matrix
burners have porous or perforated refractory plates
mounted on cast iron or formed steel plenum chambers.
The refractory material may be porous ceramic, refractory
blanket, ported ceramic, stainless steel, or metallic
screens. Typically, like impingement burners, the
porous matrix sources offers a temperature of 1,200
to 1,900°F and an intensity of 10,000 to 50,000
BTUs per hour per square foot. They typically appear
red to orange during operation, heat up in 15 to 90
seconds. Recently developed porous matrices of woven
ceramic fiber can heat-up and cool-down in seconds.
Porous matrix burners are resistant to thermal and
physical shock, and have a typical radiant efficiency
of 30 to 60%. Porous matrix burners typically have
the highest radiant efficiency of the gas-fired infrared
fuel and air mixture, supplied under pressure to the
plenum chamber, passes through the porous matrix to
burn on the surface facing the load. Combustion occurs
evenly on the exposed surface, heating it to incandescence.
As the surface heats up, the flame recedes into the
matrix, which adds radiant energy to the flame. Modulating
the fuel input provides about a 3:1 turndown capability
in oven heating intensity. (Turndown is a ratio of
the maximum and the minimum temperature.) Airflow,
as a result of natural convection, usually cools the
plenum chamber on the rear of the burners to prevent
pre-ignition of the combustible mixture.
sources. Catalytic sources consist of a porous
ceramic material, or blanket, impregnated with a catalyst,
such as platinum black, through which a combustible
air/gas mixture, or gas alone, is fed. Catalytic burners
are similar to porous matrix burners in construction,
appearance, and operation, but the refractory material
is usually glass or ceramic wool. Typically, the sources
offer a temperature of 600 to 1,000°F and an intensity
of 2,000 to 7,500 BTUs per hour per square foot. They
typically appear to have little color during operation,
heat up in 180 to 600 seconds, are resistant to thermal
and physical shock, and have a typical radiant efficiency
of 30 to 75%. The combustible air and gas mixture
oxidizes within the catalytic matrix at temperatures
below those normally required for combustion. As a
result, zoning is simplified because fewer safety
devices are required. No visible flame is produced.
As a result, these burners provide low-to-moderate
intensities. And the burners must include an alternate
heat source, usually electric heating elements, to
preheat the catalyst before operation with gas.
tube and panel sources. Radiant tube or panel
sources are internally fired metal tubes or panels.
Radiant tubes have a burner at one end firing down
the tube. Typically, the sources offers a temperature
of 400 to 1,200°F and an intensity of 1,000 to
10,000 BTUs per hour per square foot. They typically
operate at surface temperatures up to 1,200°F.
They typically appear red or have little color during
operation, heat up in 300 to 600 seconds, are resistant
to thermal and physical shock, and have a typical
radiant efficiency of 25 to 50%. Radiant panel ovens,
sometimes called "radiant walls", surround
the parts to be heated with a metal enclosure. Radiation
and hot combustion by-products, scrubbing the surface
of the enclosure, heat the exterior of the enclosure
facing the load. Infrared emission heats the parts
in the interior of the enclosure. Combustion by-products
can be vented or ducted to the convection portion
of the oven.
infrared ovens are common in a variety of applications.
Impingement and porous matrix burners are great for
ovens requiring large amounts of heat input, like
of large, heavy parts. Catalytic burners are great
for liquid coating
applications and thermoforming.
Regardless of the application, all well designed gas
infrared ovens exhibit the following characteristics:
Precise layout and distribution of sources. To incorporate
shape factors, overcome any edge effect, and provide
greater flexibility and zoning.
Insulated reflective panels to reradiate heat. To
provide reradiation even when panels may be dirty.
Non-contact temperature sensors for control. To
provide the optimum in temperature control.
Custom control. To meet the specific needs of the
process and the operators.
Safety. Adherence to all FM, IRI, OSHA and particularly
all NFPA standards and regulations.
also electric infrared